As a printer of an electrophotographic type, there is known a printer including a photosensitive member on which an electrostatic latent image is formed and an exposure device that forms an electrostatic latent image on a surface of the photosensitive member by scanning laser beam based on image data to the photosensitive member.
As the exposure device provided to the printer, related-art shows an optical scanning device which has a light source unit that emits a light beam, a polygon scanner that deflects and scans the light beam emitted from the light source unit and an optical box that accommodates therein the light source unit and the polygon scanner.
In the related-art optical scanning device, both the light source unit and the polygon scanner are fixed to a bottom face part of the optical box. Also, the bottom face part is provided with ribs that surround the polygon scanner.